De-icing coating for evaporator

ABSTRACT

A refrigeration appliance includes a body defining a compartment, and an evaporator configured to flow air from the compartment over a heat exchange surface. The evaporator has a deicing nanocoating coated on a portion of the heat exchange surface. The refrigeration appliance also includes an evaporator fan directing cooled air from the evaporator to the compartment. The deicing coating is a hydrogel forming a coated surface on the portion of the heat exchange surface with an ice nucleation temperature of −15 to −40 degrees C. and a water contact angle of 100 to 140 degrees.

TECHNICAL FIELD

The present disclosure relates to a refrigeration appliance, and more specifically, a de-icing coating for use in a refrigeration appliance.

BACKGROUND

Household appliances, such as refrigeration appliances, freezers, and combination refrigerators with freezers, have various components that operate together to cool the compartments within the appliance body. Refrigeration appliances may circulate refrigerant through an evaporator to change the refrigerant from a liquid state to a gas state via evaporation in order to maintain a low temperature within the compartments. Conventional refrigeration appliances are challenged between balancing compressor off-cycles which keep the evaporator coils free of frost and ice and ensuring proper functioning of the conventional deicing system, including the defrost timer which allows for clearing of frost and ice on the evaporator. The defrost timer initiates an air-defrost period by shutting off the compressor, while the evaporator fan continue to operate, with the defrost timer ensuring a clear evaporator coil by periodically implementing the off-cycles for the compressor. The air-defrost period facilitates the melting of frost on the finned evaporator coil surface. However, conventional systems use room temperature air, which takes significant time for defrosting and may limit performance of the condenser.

A conventional refrigeration appliance that also includes a freezer (e.g., a combination appliance) may include a heat source or a plurality of heat sources (e.g., a copper rod heating element positioned around the evaporator) to defrost components of the freezer and prevent ice buildup. For example, a conventional deicing system includes defrost heaters (e.g., heating coils, rod shape heating elements, etc.) positioned by an evaporator for defrosting the evaporator. For example, aluminum heating coils are typically included in the refrigeration appliance. However, conventional heating coils have limited thermal, structural, and mechanical properties and high-power requirements within the working environment, and as a result are limited by performance constraints and current leakage. For example, the heat generated cannot reach the central region of the evaporator where ice forms, thus taking additional time to deice Moreover, conventional heating coils have limited effective surface area due to air gaps between neighboring coils, resulting in heat transfer losses which can limit appliance efficiency and increase overall power consumption.

SUMMARY

According to one or more embodiments, a refrigeration appliance includes a body defining a compartment, and an evaporator configured to flow air from the compartment over a heat exchange surface. The evaporator has a deicing nanocoating coated on a portion of the heat exchange surface. The refrigeration appliance also includes an evaporator fan directing cooled air from the evaporator to the compartment. The deicing coating is a hydrogel forming a coated surface on the portion of the heat exchange surface with an ice nucleation temperature of −15 to −40 degrees C. and a water contact angle of 100 to 140 degrees.

According to at least one embodiment, the portion of the heat exchange surface may include heat exchange fins of the evaporator. In some embodiments, the portion of the heat exchange surface may include both coil surfaces and heat exchange fins of the evaporator. In at least one embodiment, the deicing coating may include a thermoresistive material dispersed therein. In further embodiments, the thermoresistive material may be carbon or graphene oxide. In certain further embodiments, the thermoresistive material may be carbon nanotubes. In one or more embodiments, the hydrogel may be a silica gel. In at least one embodiment, the ice nucleation temperature may be −20 to −30 degrees C.

According to one or more embodiments, an evaporator for a refrigeration appliance includes an evaporator configured to flow air from a refrigeration compartment over a heat exchange surface and to the refrigeration compartment, with the heat exchange surface including coil surfaces, evaporator fins, or combinations thereof, and a deicing nanocoating on at least a portion of the heat exchange surface. The deicing coating forms a coated surface on the at least a portion of the heat exchange surface, with the coated surface having an ice nucleation temperature of −15 to −40 degrees C. and a water contact angle of 100 to 140 degrees.

According to at least one embodiment, the portion of the heat exchange surface may include the evaporator fins. In one or more embodiments, the deicing coating may be a hydrogel layer formed from a selected monomer, water-soluble initiator, and cross-linker. In at least one embodiment, the deicing coating may include a thermoresistive material dispersed therein. In further embodiments, the thermoresistive material may be carbon or graphene oxide. In certain further embodiments, the thermoresistive material may be carbon nanotubes. In at least one embodiment, the ice nucleation temperature may be −20 to −30 degrees C.

According to one or more embodiments, a method of defrosting an evaporator includes coating a portion of a heat exchange surface of an evaporator with a hydrogel-based deicing coating to form a coated surface with an ice nucleation temperature of −15 to −40 degrees C. and a water contact angle of 100 to 140 degrees, and operating the evaporator during a defrost cycle such that ice buildup is inhibited on the hydrogel-based deicing coating.

According to at least one embodiment, the method may further include formulating the hydrogel-based deicing coating from a selected monomer, water-soluble initiator, and cross-linker. In one or more further embodiments, formulating the hydrogel-based deicing coating may further include dispersing a thermoresistive material therein. In certain further embodiments, the thermoresistive material may be carbon or graphene oxide. In at least one embodiment, the ice nucleation temperature may be −20 to −30 degrees C.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a refrigeration appliance, according to an embodiment;

FIG. 2A is a schematic illustration of a freezer compartment with a de-icing system of the refrigeration appliance of FIG. 1 ; and

FIG. 2B is a schematic cross-section taken along 2B-2B′ of the freezer compartment of FIG. 2A.

DETAILED DESCRIPTION

As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention.

Conventional deicing systems typically implement a defrost cycle to de-ice and defrost the evaporator. Among the goals of defrosting as previously discussed, the deicing system may further be designed to minimize heat gain or reduce space temperature fluctuations caused by the defrost cycles. As such, conventional deicing systems may run two to four defrost cycles per day, however, this may not be enough for unique space usage, such as refrigeration appliances with blast coolers and freezers, or other refrigeration applications with high product temperature pull-down loads. Additionally, defrosting requirements may vary throughout the week, which may place additional burden on the overall performance of the refrigeration appliance. Thus, conventional defrost heaters configured as rod heating elements exhibit higher power consumption, and, due to the uneven heat spreading, may lead to frost blocking rotation of an evaporator fan resulting in diminished cooling performance.

Furthermore, conventional deicing systems have generally limited defrosting ability due to the localized heating sources Although multiple defrost heaters may be included to provide heat to the surface of the evaporator, using multiple defrost heaters increases the power usage and heat gain in the refrigeration appliance. Moreover, because defrosting heaters provide a localized heating source, uneven frosting and defrosting on the evaporator can occur, especially if only a single defrosting heater is used, leading to performance limitations. As such, the defrost cycle performance for deicing systems needs improvements in even heating, while exhibiting minimal heat gain and reduction in temperature fluctuations.

According to one or more embodiments, a refrigeration appliance includes a deicing coating for improving defrosting performance. The deicing coating is a thin film (e.g., a thickness of 0.05 microns to 150 microns) nanocoating formed of a selected monomer, initiator, and cross-linker that can efficiently de-ice the refrigerator evaporator and limit ice nucleation thereon and is mechanically stable for coating complex geometries of the evaporator surface. The deicing coating can further melt ice via thermoresistive heating across the coating. The thickness of the deicing coating may be selected based on the surface area being covered by the deicing coating as well as the coating pattern geometry (e.g., flat, interdigitated, circular disks, or random shape pads) to be heated via thermoresistive heating. The deicing coating is formulated from a multi-functional anti-icing hydrogel that is modified for ion-specificity and hydrophobicity, and includes a thermoresistive material that generates heat upon application of current, to form the deicing coating. The deicing coating facilitates performance of the deicing system and the efficiency of the defrosting cycles by inhibiting ice nucleation, preventing ice propagation, and reducing ice adhesion as a result of improved heat transfer from the coating to the neighboring areas. Since the coating is in direct contact with iced surfaces, without any air medium in-between, the deicing is more efficient than conventional rod heating elements which have air between the rod heating elements and the surface to be de-iced. Also, although conventional solutions may address a single stage of the ice formation process, the conventional solutions may have limited performance due to the constraints of positioning of the heating elements. As such, the deicing coating described herein can be applied to complex evaporator surfaces and heated via thermoresistive heating to prevent ice formation and propagation.

Referring to FIG. 1 , an example of a refrigeration appliance 100 is shown. The refrigeration appliance 100 may be any household or commercial refrigeration appliance including, but not limited to, refrigerators, freezers, chillers, and combinations thereof, and hereinafter is referred to refrigeration appliance 100. The refrigeration appliance 100 may include various compartments to form the refrigeration appliance 100, including, but not limited to, freezer compartments, refrigerator compartments, chiller compartments, and combinations thereof. In the example shown in FIG. 2 , the refrigeration appliance 100 includes a freezer compartment 110 with a freezer door 112 and a refrigerator compartment 120 with a refrigerator door 122. The refrigeration appliance 100 may be constructed in any suitable manner, and the depiction of a refrigeration appliance 100 with a freezer compartment 110 configured side-by-side with the refrigerator compartment 120 is not intended to be limiting. For example, the refrigeration appliance 100 may have a freezer compartment 110 as a drawer and a refrigerator compartment 120 with French doors, or in other examples, have the refrigerator compartment 120 below a freezer compartment 110, and may further have any suitable number of doors, compartments, and drawers to configure the refrigeration appliance 100. In one or more embodiments, as shown in the example of FIG. 2 , the refrigeration appliance 100 may include a dispenser 230 for dispensing water and/or ice from the refrigeration appliance 100. Although shown in the example of FIG. 2 , the dispenser 230 may be omitted or be included internally within the refrigerator compartment 120 or the freezer compartment 110, and depiction on the exterior is in the freezer door 112 is not intended to be limiting. The refrigeration appliance 100 may include any suitable mechanisms for operation, including, but not limited to, an evaporator 140, evaporator fan 145, a condenser (not shown), a compressor (not shown), and the like, and the only relevant components will be shown and described in further detail with reference to FIGS. 2A-B.

The relevant components for the freezer compartment 110 of the refrigeration appliance 100 are schematically shown in FIG. 2A, and as a schematic cross-section taken along 2B-2B′ of the freezer compartment 110 in FIG. 3B. Referring collectively to FIGS. 2A-2B, the refrigeration appliance 100 includes an evaporator 140 configured to cool air A1 from the freezer compartment 110 by flowing the air flow A2 over the coils and fins forming a heat exchange surface 142 of the evaporator 140, while refrigerant flows therethrough. The refrigeration appliance 100 further includes an evaporator fan 145 positioned to facilitate and draw the air flow A2 from the evaporator 140 and flow cold air A3 into the freezer compartment 110 via freezer vents 114. A drain pan 150 is included at the base of the freezer compartment 110 to collect and drain water from the refrigeration appliance 100 that forms upon defrosting of the evaporator 140.

The heat exchange surface 142 of the evaporator 140 includes a deicing nanocoating 200 on at least a portion of the heat exchange surface 142, the details of the deicing nanocoating 200 which will be described in further detail below. The at least a portion of the heat exchange surface 142 may be determined, in some embodiments, based on susceptibility to ice formation. In other embodiments, the at least a portion may be chosen based on the shape or geometry of the selective area to form a thermoresistive network of the deicing nanocoating 200.

For example, the deicing nanocoating 200 may be applied to the entirety of the coil surfaces of the evaporator 140, on the fins of the evaporator 140, or on combinations thereof. Additionally or alternately, the deicing nanocoating may be applied to selective areas of the coil surfaces, the fins, or combinations thereof such that portions of the heat exchange surface 142 are coated with the deicing nanocoating 200. For instance, the deicing nanocoating 200 may cover a percentage of the heat exchange surface 142. In one non-limiting example, the deicing nanocoating 200 may cover 30-100% of the heat exchange surface 142. In other embodiments, 40-100% of the heat exchange surface 142, and in yet further embodiments, 50-100% of the heat exchange surface 142. The deicing nanocoating 200 may lower the ice nucleation temperature of the coated surfaces of the heat exchange surface 142 to which the deicing nanocoating 200 is applied. In certain embodiments, the coating of the heat exchange surface 142 allows the refrigeration appliance 100 to consume less power and have a faster impact during a defrost cycle than conventional heating elements because of the direct heating at the heat exchange surface 142. Generally, the power rating is based on the overall thermal resistance of the coating applied, however the deicing nanocoating 200 requires less power than a defrost heater in conventional refrigeration appliances and achieves improved defrosting.

The deicing nanocoating 200 may be a single layer applied to the at least a portion of the heat exchange surface or may comprise a plurality of layers to form the deicing nanocoating 200. In certain embodiments, the deicing nanocoating 200 may have an overall thickness (e.g., of a single layer or multiple layers) of 0.03 microns to 400 microns, in other embodiments, 0.04 microns to 200 microns, and in yet further embodiments 0.05 microns to 150 microns.

The deicing nanocoating 200 may be an anti-icing hydrogel thin film coating of a selected monomer, initiator, and cross-linker coated on at least portions of the heat exchange surface 142 of the evaporator 140 that lowers ice nucleation temperature on the coated surface while suppressing the rate of ice propagation and reducing the ice adhesion to the coated surface. Moreover, the hydrogel-based deicing nanocoating 200 is flexible based on the water content during development such that the deicing nanocoating 200 can coat complex structures and contours of the heat exchange surface 142 (e.g., fins), and behaves similarly flexible to natural tissue. The water content during formation of the hydrogel coating is based on using a pre-polymerized polymer, such as, but not limited to a 2-system based pre-polymerized polymer such as pre-polymerized polyvinyl alcohol, polyethylene glycol, sodium polyacrylate, acrylate polymers and copolymers thereof.

The hydrogel may be formed in any suitable manner, including, but not limited to, inverse-suspension.

The initiator may be any suitable initiator, such as water-soluble initiators or oil-soluble initiator, however, in at least one embodiment, a water-soluble initiator is used to form the hydrogel. In other examples, a silica gel may be used to form the deicing nanocoating 200.

In one or more embodiments, the deicing nanocoating 200 includes a thermoresistive material, such as, but not limited to carbon or graphene oxide. The thermoresistive material, such as carbon (e.g, in nanotube form or other nanoparticle form) or graphene oxide, may be loaded in, in some embodiments 0.25 to 2% loading by weight of the nanocoating, in other embodiments 0.4 to 1.75%, and in yet other embodiments 0.5 to 1.5%. The thermoresistive material may, in certain embodiments, have a loading concentration by weight of 0.05 to 5.5%, in other embodiments 0.075 to 5.25%, and in yet further embodiments, 0.10 to 5.0% in the coating.

The cross-linker may be used when the initiator and the selected monomer are blended together. In certain examples, the cross-linker cross-links the deicing coating when the initiator and the selected monomer are blended together using a 3D blender (for example, for about 1.5 to 2.5 hours).

During formation of the deicing nanocoating 200, when the initiator is loaded in the dispersed (aqueous) phase, each particle of the deicing nanocoating 200 contains all the reactive species and therefore behaves like an isolated micro-batch. The resulting micro-spherical particles are removed by filtration or centrifugation from the continuous organic phase and dried. Upon drying, these particles form a free-flowing powder, which can be used with the pre-polymerized polymer to develop the deicing nanocoating 200 as a thin-film nanocoating for application to the evaporator 140 to form a thermoresistive network of the deicing nanocoating 200. The deicing nanocoating is applied to the selective portions in any suitable manner for applying the free flowing powder, and then undergoes pre-baking and post-baking processes at 105° C. and 180° C., respectively.

The deicing nanocoating 200, upon application to the heat exchange surface 142, forms a coated surface of the evaporator 140 with an ice formation or, interchangeably, nucleation temperature, in certain embodiments of −15° C. to −40° C., in other embodiments −20° C. to −35° C., and in yet further embodiments −25° C. to −30° C. In yet further embodiments, the ice nucleation temperature may be −20 to −30° C.

Ice may still form on uncoated portions of the heat exchange surface 142, and moreover, may still form on the coated portions of the heat exchange surface 142 based on the conditions. However, the air flow A2 through the evaporator 140 during operation may be sufficient to blow-off any buildup ice formation without any degradation to the hydrogel film applied based on the hydrophobicity of the hydrogel film (e.g., the deicing nanocoating 200 has a water contact angle of 100 to 140 degrees, in some embodiments, and 110 to 130 degrees in other embodiments). Furthermore, the thermoresistivity of the deicing nanocoating 200 upon application of current allows the deicing nanocoating 200 to be heated to at least the same temperature as conventional copper wire and steel rod heating elements with less electric power consumption than the conventional copper wire and steel rod heating elements to melt ice buildup on the evaporator 140 surfaces that are susceptible to frost.

With regard to the deicing nanocoating 200, the deicing nanocoating 200 forms the thermoresistive network for melting ice buildup and preventing ice nucleation and formation on the surface of the deicing nanocoating 200. The thermoresistive network formed by the deicing nanocoating 200 may include a plurality of interconnected heating elements on the evaporator and/or fin surface. These heating elements may define, in some embodiments, discrete heating areas that may be independently controlled for heating as based on presence of ice, or frequency of ice buildup in that particular location. The interconnected heating elements may be formed of the deicing nanocoating 200, and may, in some embodiments, have a layered structure of film layers (e.g., thin film layers). At least one layer of the deicing nanocoating 200 includes an initiator that is a thremoresistive element such as carbon nanotubes or graphene oxide nanoparticles to provide thermal diffusion with less power consumption than conventional rod-type heating elements. As such, independent heating elements may be selectively activated to increase the heating capability within a particular area of the evaporator 140, thus forming a conformal heating profile over a larger area using a network of connected heating elements.

The deicing nanocoating 200 may form the thermoresistive network and be electrically connected in any suitable manner, such as, but not limited to, by copper connectors or other wiring, buses, or interconnects to flow current to the deicing nanocoating 200 to produce heat. In embodiments where the deicing nanocoating is continuous across the evaporator and/or fin surface to form the thermoresistive network, electrode(s) may be positioned in any suitable manner for supplying current to the deicing nanocoating 200. In certain embodiments, the electrode may be silver. In embodiments where the thermoresistive network is formed from discrete interconnected heating elements, each thermoresistive heating element may also include an electrode, or pair of electrodes, for applying the electrical conduction uniformly. In one or more embodiments, the electrodes are positioned on opposite sides of the respective heating element to allow current to flow through the heating element from one of the electrodes to the other electrode, such that heat is generated in the heating element.

The resistance of the deicing nanocoating 200 may be any suitable resistance to limit ice formation and melt ice buildup on the evaporator 140, without otherwise affecting the power consumption of the refrigeration appliance 100. For example, regions of the deicing nanocoating 200 that form the thermoresistive network (i.e., the interconnected heating elements) may independently have any suitable resistance for the desired heat generation as based on the size of the heating element and location of the coating. In some examples, the coating may have individual heating elements with or an overall resistance of 10 to 50Ω, in other embodiments, 1.0 to 35Ω, and in yet other embodiments, 20 to 30Ω.

In certain embodiments, combining heating elements of similar resistance may result in a higher temperature observed in the deicing nanocoating 200 based on the current applied. Furthermore, the deicing nanocoating 200 may include any number of electrically insulative layers (not shown) or components to limit electrical leakage while being thermally conductive to allow uniform heating of the deicing nanocoating 200 across the heat exchange surface 142. The electrically insulative material may have a thermal conductivity in some embodiments, between 0.015 W/mK to 0.5 W/mK, in other embodiments, between 0.020 W/mK to 0.4 W/mK, and in yet other embodiments, between 0.025 W/mK to 0.30 W/mK. The electrically insulative material improves control over the selective activation of the deicing nanocoating 200 and may cover the electrical connections for the thermoresistive network of the deicing nanocoating 200.

According to one or more embodiments, a refrigeration appliance with a deicing nanocoating for defrosting an evaporator is provided. The deicing nanocoating is a hydrogel film coated on the heat exchange surface of the evaporator, with sufficient flexibility to coat the complex structures of the surface (e.g., fins) that includes a thermoresistive heating element to heat the surface of the evaporator and prevent ice formation and melt ice build up on the evaporator. The deicing nanocoating is formed via a selected monomer, initiator, and cross-linker as hydrogels that can be applied to the heat exchange surface and lower ice nucleation temperatures of the coated surface while suppressing ice propagation and lowering ice adhesion.

Except where otherwise expressly indicated, all numerical quantities in this disclosure are to be understood as modified by the word “about”. The term “substantially,” “generally,” or “about” may be used herein and may modify a value or relative characteristic disclosed or claimed. In such instances, “substantially,” “generally,” or “about” may signify that the value or relative characteristic it modifies is within ±0%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5% or 10% of the value or relative characteristic (e.g., with respect to transparency as measured by opacity). Practice within the numerical limits stated is generally preferred. Also, unless expressly stated to the contrary, the description of a group or class of materials by suitable or preferred for a given purpose in connection with the disclosure implies that mixtures of any two or more members of the group or class may be equally suitable or preferred.

As referenced in the figures, the same reference numerals may be used herein to refer to the same parameters and components or their similar modifications and alternatives. For purposes of description herein, the terms “upper,” “lower,” “right,” “left,” “rear,” “front,” “vertical,” “horizontal,” and derivatives thereof shall relate to the present disclosure as oriented in FIG. 1 . However, it is to be understood that the present disclosure may assume various alternative orientations, except where expressly specified to the contrary. It is also to be understood that the specific devices and processes illustrated in the drawings and described in the following specification are simply exemplary embodiments of the inventive concepts defined in the appended claims. Hence, specific dimensions and other physical characteristics relating to the embodiments disclosed herein are not to be considered as limiting, unless the claims expressly state otherwise. The drawings referenced herein are schematic and associated views thereof are not necessarily drawn to scale.

While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention. 

1. A refrigeration appliance comprising: a body defining a compartment; an evaporator configured to flow air from the compartment over a heat exchange surface, the evaporator having a deicing nanocoating coated on a portion of the heat exchange surface; and an evaporator fan directing cooled air from the evaporator to the compartment, wherein the deicing coating is a hydrogel with a thermoresistive material dispersed therein forming a coated surface on the portion of the heat exchange surface with an ice nucleation temperature of −15 to −40 degrees C. and a water contact angle of 100 to 140 degrees, and, upon application of a current to the de-icing coating, the thermoresistive material heats the coated surface to melt ice formed thereon.
 2. The refrigeration appliance of claim 1, wherein the portion of the heat exchange surface includes heat exchange fins of the evaporator.
 3. The refrigeration appliance of claim 1, wherein the portion of the heat exchange surface includes both coil surfaces and heat exchange fins of the evaporator.
 4. (canceled)
 5. The refrigeration appliance of claim 1, wherein the thermoresistive material is carbon or graphene oxide.
 6. The refrigeration appliance of claim 5, wherein the thermoresistive material is carbon nanotubes.
 7. The refrigeration appliance of claim 1, wherein the hydrogel is a silica gel.
 8. The refrigeration appliance of claim 1, wherein the ice nucleation temperature is −20 to −30 degrees C.
 9. An evaporator for a refrigeration appliance comprising: a heat exchange surface including coil surfaces, evaporator fins, or combinations thereof, with the evaporator configured to flow air from a refrigeration compartment over the heat exchange surface and to the refrigeration compartment; and a deicing nanocoating on at least a portion of the heat exchange surface to form heating elements associated with a discrete heating area, the deicing coating including a thermoresistive material dispersed therein and forming a thermoresistive network by interconnection of the heating elements, wherein the deicing coating forms a coated surface on the at least a portion of the heat exchange surface, the coated surface having an ice nucleation temperature of −15 to −40 degrees C. and a water contact angle of 100 to 140 degrees, and upon selective application of a current to the heating elements, melting ice build-up associated with the discrete heating area.
 10. The evaporator of claim 9, wherein the portion of the heat exchange surface includes the evaporator fins.
 11. The evaporator of claim 9, wherein the deicing coating is a hydrogel layer formed from a selected monomer, water-soluble initiator, and cross-linker.
 12. (canceled)
 13. The evaporator of claim 9, wherein the thermoresistive material is carbon or graphene oxide.
 14. The evaporator of claim 9, wherein the thermoresistive material is carbon nanotubes.
 15. The evaporator of claim 9, wherein the ice nucleation temperature is −20 to −30 degrees C.
 16. A method of defrosting an evaporator, the method comprising: coating a portion of a heat exchange surface of the evaporator with a hydrogel-based deicing coating including a thermoresistive material dispersed therein to form a coated surface associated with a discrete heating area with an ice nucleation temperature of −15 to −40 degrees C. and a water contact angle of 100 to 140 degrees; and operating the evaporator during a defrost cycle such that a current is selectively applied to the coated surface to melt ice buildup on the hydrogel-based deicing coating in the discrete heating area.
 17. The method of claim 16, further comprising formulating the hydrogel-based deicing coating from a selected monomer, water-soluble initiator, and cross-linker.
 18. The method of claim 17, wherein formulating the hydrogel-based deicing coating further includes dispersing the thermoresistive material therein.
 19. The method of claim 18, wherein the thermoresistive material is carbon or graphene oxide.
 20. The method of claim 16, wherein the ice nucleation temperature is −20 to −30 degrees C. 